Lazy initialization of the rendering thread in OfflineAudioContext

third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp

 /*
  * Copyright (C) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
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  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 212 matching lines @@
   return ScriptPromise();
 }
 
 ScriptPromise OfflineAudioContext::suspendContext(ScriptState* script_state,
                                                   double when) {
   DCHECK(IsMainThread());
 
   ScriptPromiseResolver* resolver = ScriptPromiseResolver::Create(script_state);
   ScriptPromise promise = resolver->Promise();
 
-  // The render thread does not exist; reject the promise.
-  if (!DestinationHandler().OfflineRenderThread()) {
-    resolver->Reject(DOMException::Create(kInvalidStateError,
-                                          "the rendering is already finished"));
-    return promise;
-  }
-

[hongchan, 2017/05/19 17:35:06]

The existence of thread and being able to schedule a context suspend are
orthogonal. Not sure why this code was here in the first place.

WDYT?

[Raymond Toy, 2017/05/19 19:37:54]

Based on the comments, when rendering is done, the thread goes away, and we're
rejecting because you can't suspend a context that as already finished
rendering.

If that's correct, can you check if we have a test for this?  If we don't we
probably should.

   // The specified suspend time is negative; reject the promise.
   if (when < 0) {
     resolver->Reject(DOMException::Create(
         kInvalidStateError,
         "negative suspend time (" + String::Number(when) + ") is not allowed"));
     return promise;
   }
 
   // Quantize (to the lower boundary) the suspend time by the render quantum.
   size_t frame = when * sampleRate();
@@ skipping 202 matching lines @@
 
   // Note that the GraphLock is required before this check. Since this needs
   // to run on the audio thread, OfflineGraphAutoLocker must be used.
   if (scheduled_suspends_.Contains(CurrentSampleFrame()))
     return true;
 
   return false;
 }
 
 }  // namespace blink